The invention relates generally to alarm systems, and deals more particularly with a sonic alarm system which detects intrusion into a defined space, relative movement between the alarm system and a reference point, and breakage of a window.
Various types of alarm systems were previously known. For example, an electric eye detects the presence of an object between a light source and a detector. An infrared sensor detects the presence of a warm body in the field of the sensor. Sound level alarm systems detect a source of sound, and vibration alarm systems detect a source of vibration.
One problem with previously known alarm systems is false positives. For example, a sound level alarm system may be inadvertently activated by a loud noise outside of a room or automobile in which the system is installed, especially if a window or door of the room or automobile is open. A vibration sensitive alarm system may be inadvertently activated by a remote source of vibrations, or non-harmful contact with an automobile in which the system is installed. An infrared alarm system may be inadvertently activated by a heat source outside of a room or automobile in which the system is installed if the sensor is aligned with an open window and the heat source is located outside the window.
Accordingly, a general object of the present invention is to provide a reliable alarm system.
A more specific object of the present invention is to provide a reliable alarm system which can he used in an automobile, truck, room, or other defined space.
Another specific object of the present invention is to provide an alarm system which minimizes false positives.
Still another specific object of the present invention is to provide an alarm system which can detect intrusion through an open door, open window or predefined boundary in space without being activated by moving or warm bodies beyond the opening or boundary.
Yet another specific object of the present invention is to provide an alarm system which can detect opening of a door, a window, a vehicle hood, a vehicle trunk lid, or the elevation of an automobile or truck.
Still another object of the present invention is to provide an alarm system which can detect intrusion into a predefined space which is not enclosed by physical boundaries.